Method of making an electrically released electromagnetic friction brake

ABSTRACT

An electromagnetic friction brake whose components are held in assembled relationship by pins which are received with a press fit within holes in an electromagnet and an end plate and which are received with a loose fit within holes in an armature. By virtue of the pins, an assembly gage may be used to automatically establish an air gap of desired width between the armature and the electromagnet when the brake is assembled.

This is a division of application Ser. No. 828,525, filed Aug. 29, 1977now U.S. Pat. No. 4,156,478.

BACKGROUND OF THE INVENTION

This invention relates to an electrically released brake of the type inwhich an electromagnet, an armature, a ring of friction material and anend plate are sandwiched together in an assembly. The ring of frictionmaterial is rotatable relative to the other elements of the assembly andis adapted to be connected to a driven member such as a rotatable shaftwhose motion is to be retarded by the brake.

Upon energization of the electromagnet, the armature is drawn away fromthe ring of friction material and toward the electromagnet to releasethe brake. When the electromagnet is de-energized, springs associatedwith the electromagnet press the armature against the friction materialand press the friction material against the end plate so as to apply thebrake and frictionally retard rotation of the shaft.

To help optimize the braking torque and service life of a given brake,it is necessary to establish an air gap of predetermined axial widthbetween the electromagnet and the armature. In prior brakes of thisgeneral type, the width of the air gap is established by manuallyadjusting screws or the like which hold the electromagnet, the armatureand the end plate in assembled relationship. Trial and error is requiredto make such adjustments and thus the assembly procedure is relativelyexpensive and, in addition, the gap is not always established with theoptimum width.

SUMMARY OF THE INVENTION

The general aim of the present invention is to provide a new andimproved brake of the foregoing character in which an air gap of precisepredetermined width may be established between the electromagnet and thearmature automatically as an incident to these elements being assembledwith the friction ring and the end plate, the brake thereby lendingitself to quick, easy and accurate assembly.

A more detailed object is to provide a brake whose components are heldin assembled relationship by pins which are pressed into theelectromagnet and the end plate, such pins enabling the use of anassembly gage for establishing an air gap of precise width when thecomponents are pressed together.

A further object of the invention is to provide a new and simplifiedmethod for assembling the components of a brake, the method enabling thebrake to be assembled in less time than prior brakes and eliminating theneed of using trail and error adjustments to establish the air gap.

The invention also resides in the provision of a unique brake having amulti-part friction ring which enables the brake to develop high brakingtorque and yet still experience a long service life.

These and other objects and advantages of the invention will become moreapparent from the following detailed description when taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation of a typical motor equipped with a new andimproved brake incorporating the unique features of the presentinvention, the brake being shown in a section taken substantially alongthe line 1--1 of FIG. 2.

FIGS. 2 and 3 are cross-sections taken substantially along the lines2--2 and 3--3, respectively, of FIG. 1.

FIG. 4 is a fragmentary cross-section showing one step of assembling thebrake.

FIG. 5 is a view similar to FIG. 4 but shows a subsequent step ofassembling the brake.

FIG. 6 is a cross-section taken substantially along the line 6--6 ofFIG. 4.

FIG. 7 is a view similar to FIG. 5 but shows a modified brake.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in the drawings for purposes of illustration, the invention isembodied in an electromagnetic friction brake 10 of the type which may,for example, be attached to the end of an electric motor 11 to stop theshaft 13 of the motor at selected times. The brake includes an end plate14 which may be anchored to the motor by screws 15 and further includesa hub 16 adapted to be fastened to the motor shaft by a set screw 17. Asis conventional, the hub is formed with an outer periphery which is ofhexagonal or other non-circular cross-section (see FIG. 2).

The brake 10 further includes a ring 19 of friction material adapted torotate with the shaft 13 and the hub 16 and adapted to rotate relativeto the end plate 14. The inner periphery of the ring is of hexagonalshape to enable the ring to turn with the hub.

Braking of the shaft 13 is effected in response to the de-energizationof an electromagnet 20 (FIG. 1). Herein, the electromagnet includes anannular shell 21 made of cast iron or the like and enclosing an annularcoil or winding 23 which is adapted to be connected by leads (not shown)to a suitable voltage source. When the coil is energized, an annulararmature 24 is drawn away from the friction ring 19 and into engagementwith the pole faces 25 of the shell 21 so as to release the frictionring and enable the shaft 13 to rotate. Upon de-energization of thecoil, springs 26 press the armature 24 against one face of the frictionring and press the other face of the friction ring against the end plate14 to stop the shaft. In the present instance, the springs are of thecoiled compression type and four such springs are located withinangularly spaced openings 27 formed in the shell 21.

When the brake 10 is being manufactured, it is important to assemble thecomponents in such a manner that an air gap 30 (FIG. 1) of a preciselypredetermined axial width will exist between the armature 24 and thepole faces 25 of the shell 21 when the coil 23 is de-enerized. In one ofits aspects, the present invention contemplates the provision of aunique brake which is constructed so that an air gap 30 of a preciselypredetermined axial width may be established automatically between thearmature 24 and the pole faces 25 of the shell 21 when the components ofthe brake are assembled. In another of its aspects, the inventioncontemplates a novel method of assembling the brake, the methodeliminating the need of manually adjusting the components to establishthe air gap and thus enabling the brake to be assembled with greaterpreciseness and at lower cost than prior brakes of the same generaltype.

More specifically, the brake 10 is characterized by pins 35 which areadapted to be inserted with a tight press fit into angularly spacedholes 36 and 37 (FIG. 1) in the end plate 14 and the shell 21,respectively, and with a loose fit in holes 38 in the armature 24.Herein, four such pins are employed and each includes a head 40 (FIGS. 1and 4) which is significantly larger than the holes 36, a first roughportion 41 whose diameter is slightly larger than the diameter of theholes 36, a smooth intermediate portion 42 having a diametersignificantly smaller than the diameter of the holes 36 and 38, a secondrough portion 43 whose diameter is less than the diameters of the holes36 and 38 but greater than the diameter of the holes 37, and a tip 44having a diameter smaller than the diameter of the holes 37. The roughportions 41 and 43 may be created by forming straight knurls along theappropriate portions of each pin.

In the assembled brake 10, the head 40 of each pin 35 engages the endplate 14 while the knurled portions 41 and 43 are received with a pressfit in the holes 36 and 37, respectively, so as to hold the end plateand the shell 21 in assembled relationship. The smooth intermediateportion 42 of each pin, however, is received in the hole 38 with a loosefit to enable the armature 24 to shift back and forth when the coil 23is energized and de-energized, the pins preventing the armature fromrotating. While the pins 35 are located outwardly of and do not extendthrough the friction ring 19, they do captivate the ring between the endplate 14 and the armature 24 and prevent the ring from being removedradially from between the plate and the armature. This is achieved bylocating the pins such that the spacing between adjacent pins is lessthan the diameter of the friction ring.

By virtue of the pins 35, the components of the brake 10 may beassembled quickly and easily with a press having a horizontal bolster 50(FIG. 4) and a vertically shiftable ram 51, the assembly method makinguse of a gage 53 which establishes the air gap automatically when thecomponents are assembled. In the present instance, the gage comprisestwo identical gage plates 54 and 55 (FIGS. 4 and 6) adapted to beinserted between the end plate 14 and the armature 24 and each formedwith angularly spaced semi-circular notches 56 (FIG. 6) which receivethe pins 35 when the gage plates are in place. In addition, each gageplate is formed with a comparatively large and centrally locatedsemi-circular notch 57 whose wall extends around the friction ring 19.

The axial thickness of the gage plates 54 and 55 is greater than theaxial thickness of the friction ring 19 with the difference between thetwo thicknesses determining the width of the air gap 30 between thearmature 24 and the pole faces 25 of the shell 21. Gage plates ofgreater or lesser thickness than the gage plates 54 and 55 may be usedto establish wider or narrower air gaps but the thickness of the gageplates should always be greater than the thickness of the friction ring.

To assemble the brake 10, the electromagnetic subassembly comprising theshell 21, the coil 23 and the springs 26 is placed on the bolster 50 ofthe press with the springs extending upwardly as shown in FIG. 4. Thearmature 24 then is placed on top of the springs and is located suchthat the holes 38 in the armature are alined with the holes 37 in theshell 21, the springs holding the armature in upwardly spaced relationfrom the shell. Thereafter, the friction ring 19 is placed on top of thearmature and then the end plate 14 is placed on top of the friction ringin such a position that the holes 36 in the end plate are alined withthe holes in the armature and the shell.

The pins 35 then are inserted through the holes 36 and 38 in the endplate 14 and the armature 24 and are piloted into the holes 37 in theshell 21, the reduced diameter tips 44 of the pins enabling partialinsertion of the pins into the holes 37. Thereafter, the two gage plates54 and 55 are slipped radially between the end plate 14 and the armature24 with the notches 56 in the gage plates receiving the pins 35 and withthe notches 57 receiving the friction ring 19.

With the gage plates 54 and 55 and the components of the brake 10 thusarranged, the ram 51 of the press is lowered into engagement with theheads 40 of the pins 35 and is shifted downwardly to press the knurledportions 43 of the pins into the holes 37 in the shell 21. When theknurled portions 43 of the pins reach the holes 37, continued downwardadvancement of the ram causes the armature 24, the gage plates 54 and 55and the end plate 14 to compress the springs 26 and to shift downwardlywith the pins until the armature tightly engages the pole faces 25 ofthe shell 21 and until the gage plates tightly engage the armature andthe end plate engages the gage plates. Final downward movement of theram then presses the knurled portions 41 of the pins into the holes 36and causes the heads 40 of the pins to engage the end plate 14.

With the knurled portions 41 and 43 of the pins 35 pressed into theholes 36 and 37, respectively, of the end plate 14 and the shell 21, theend plate, the gage plates 54 and 55, the armature 24 and the shell willremain in their pressed-together positions after the ram 51 has beenretracted upwardly from the pins. When the ram has been so retracted,the gage plates 54 and 55 may be pulled radially from between the endplate 14 and the armature 24. As an incident thereto, the springs 26will force the armature away from the pole faces 25 of the shell untilthe armature presses the friction ring 19 against the end plate 14, thearmature moving through a distance equal to the difference between thethickness of the gage plates and the thickness of the friction ring.Accordingly, the air gap 30 between the armature 24 and the pole faces25 of the shell 21 is precisely and automatically established at apredetermined width as an incident to the components of the brake 10being assembled.

Another embodiment of a brake 10' incorporating the features of theinvention is shown in FIG. 7 in which parts corresponding to those ofthe first embodiment are indicated by the same but primed referencenumerals. The brake 10' is particularly characterized by the fact thatit can develop higher braking torque and experience less wear than thebrake 10.

More particularly, the friction ring 19' of the brake 10' is defined byan annular metal disc 60 which is sandwiched between two annular discs61 and 62 of friction material. The metal disc 60 is formed with holes63 which receive the pins 35' with a loose fit so as to prevent themetal disc from turning while permitting that disc to slide on the pins.The two friction discs 61 and 62 are located radially inwardly of thepins and are free to turn with the hub 16'.

When the electromagnet 20' is de-energized, the armature 24' pressesagainst the friction disc 61 which, in turn, presses the metal disc 60against the friction disc 62. The latter disc is pressed against the endplate 14' and thus the brake 10' includes four pairs of surfacesdisposed in frictional engagement rather than two pairs of surfaces asin the case of the brake 10. Accordingly, the braking torque of thebrake 10' is virtually doubled and the service life of the brake issignificantly increased. The brake 10' may be assembled in the samemanner as the brake 10 as is apparent from FIG. 7.

I claim:
 1. A method of assembling a brake having a subassemblycomprising (a) a shell, (b) an annular electromagnetic coil disposedwithin said shell and (c) spring means disposed within said shell, saidbrake further having an armature, having friction material adapted torotate relative to said subassembly and said armature, and having aplate adapted to be fixed against rotation relative to said subassemblyand said armature, said armature being drawn away from said frictionmaterial and toward one face of said shell when said coil is energizedand being resiliently biased into engagement with said friction materialand pressing the latter against said plate when said coil isde-energized, said shell, said armature and said plate all being formedwith angularly spaced holes adapted to be alined with one another, saidmethod comprising the steps of, placing one face of said armature nextto said one face of said shell with the holes in said armature alinedwith the holes in said shell, placing said friction material next to theother face of said armature with the friction material located radiallyinwardly of said holes, placing one face of a gage of predeterminedaxial thickness next to said other face of said armature, the axialthickness of said gage being greater than the axial thickness of saidfriction material, placing said plate next to the other face of saidgage with the holes in said plate alined with the holes in said armatureand said shell, inserting pins into the holes in said plate, saidarmature and said shell, said pins being sized to be received with apress fit in the holes in said plate and said shell and with a loose fitin the holes in said armature, pressing said pins into said plate andsaid shell until said armature abuts said shell, said gage abuts saidarmature and said plate abuts said gage, and removing said gage frombetween said armature and said plate to enable said spring means topress said armature into engagement with said friction material and toshift said armature away from said one face of said shell by a distanceequal to the difference between the axial thickness of said gage and theaxial thickness of said friction material.
 2. A method as defined inclaim 1 in which said gage comprises at least two pieces, said gagepieces being slipped radially from between said plate and said armatureafter said pins have been pressed.